Multiparameter theatre lighting fixtures are lighting fixtures, which illustratively have two or more individually remotely adjustable parameters such as focus, color, image, position, or other light characteristics. Multiparameter lighting fixtures are widely used in the lighting industry because they facilitate significant reductions in overall lighting system size and permit dynamic changes to the final lighting effect. Applications and events in which multiparameter lighting fixtures are used to great advantage include showrooms, television lighting, stage lighting, architectural lighting, live concerts, and theme parks.
Multiparameter theatre lighting fixtures are commonly constructed with a lamp housing that may pan and tilt in relation to a base housing so that light projected from the lamp housing can be remotely positioned to project on a stage surface. The lamp housing of the multiparameter light contains the optical components such as a lamp and may include color filters for varying the color of the projected light. Commonly a plurality of multiparameter lights are controlled by an operator from a central controller. The central controller is connected to communicate with the plurality of multiparameter lights via a communication system.
U.S. Pat. No. 4,962,687 to Belliveau, describes a variable color lighting system and instrument that uses an additive color mixing method to fade from one color to another. The lighting instrument is comprised of three lamps each emitting a different wavelength of light in the colors of red, green and blue that can be added together to vary the color of the projected light.
The use of dichroic filters to color the light projected by a multiparameter theatre lighting instrument is known in the art. U.S. Pat. No. 4,392,187 to Bornhost, discloses the use of dichroic filters in a multiparameter light. Bornhorst discloses “The dichroic filters transmit light incident thereon and reflect the complement of the color of the transmitted beam. Therefore, no light is absorbed and transformed to heat as found in the prior art use of celluloid gels. The use of a relatively low power projection lamp in lights 30 and 110 substantially reduces the generation of infrared radiation which causes high power consumption and heat buildup within prior art devices.” While the use of color wheels that support multiple wavelengths of dichroic filters to color the light of a multiparameter stage light is still in common practice, it is also common practice to construct a multiparameter light having variable density dichroic filter flags that gradually color the light using a subtractive color method. The subtractive color method may use the dichroic filter flag colors of cyan, magenta and yellow to gradually and continuously vary the color of today's multiparameter stage light producing a pleasing color fade when visualized by an audience. The gradual and continuous varying of cyan, magenta and yellow in the light path of a multiparameter light is referred to as “CMY color mixing” in the theatrical art.
Present day light sources for theatrical instruments are primarily comprised of light emitting diodes (LEDs). One such theatrical instrument using a high power white LED light source is the SolaWash 2000 by High End Systems of Austin, Tex. found at https://www.highend.com/products/lighting/solawash. This high power white LED lighting instrument varies the color of the projected light using a CMY color mixing system, which is known in the art.
Theatrical Lighting Designers are becoming increasingly critical of the requirement that the color(s) and intensity of the light emitted by a first theatre lighting device is visually and measurably the same as the light emitted by a second theatre lighting device. The advent of cost effective smart phone spectrometers in the hands of savvy lighting designers now allows the designers to directly compare and capture data by spectrometer for each theatre lighting device and forward that comparison data results to the manufacture sometimes with complaints. While it is virtually impossible to obtain a measured spectrum that is identical from theatre lighting device to theatre lighting device manufacturers do strive to make improvements to their manufacturing and specification process.
The intensity and color differences of each theatrical lighting device is comprised of many different light source tolerances, optical filter tolerances, mechanical tolerances, electronic component tolerances, and lens and antireflective coating tolerances. Unfortunately the human eye is extremely sensitive to color differences in side by side comparisons which is a common installation practice of theatrical lighting devices when used during a theatrical event. The human eye can differentiate approximately ten million colors but only in a side by side comparison. Studies on how sensitive the human eye is regarding color differences of light sources have been previously been conducted. For example, see “Paper #51 Just Perceivable Color Differences between Similar Light Sources in Display Lighting Applications”, Narendran, Vasconez, Boyce, and Eklund, Lighting Research Center, Rensselaer Polytechnic Institute.
U.S. Pat. No. 5,282,121 to Bornhorst discloses an intensity feedback device 224 and a color sensor or spectrum analyzer 280 as sensor components of the apparatus disclosed in FIG. 7.
As stated in Bornhorst '121: “A light-sensitive electrical device, such as a photo diode or other suitable transducer can be used to sample the beam after it has been subjected to dimming by an intensity control mechanism, and provides intensity feedback signals to the local processor 285 for intensity control. In one embodiment, shown in FIG. 7, the intensity feedback device 224 is positioned to sample the intensity of light after the intensity control wheel 222. The intensity feedback arrangement allows a luminaire to produce a specified level of illumination. Intensity feedback may be selectively disabled in the operating system software controlling the local processor, for example in instances in which the feedback sensor might be in the shadow of a gobo or other projected image. Color Matching. A problem which arises in some applications involves color mismatch between luminaires. Lamp color calibration can vary with lamp type and can also change with time making it difficult to achieve precise color match among the luminaires of a system. To address this problem, the system according to the invention includes a color sensor or spectrum analyzer 280 for quantifying beam color. It is implemented with a linear variable filter 280a, FIG. 7, which is located to sample the beam after it has been subjected to coloring by the beam color system 221. For this purpose, it may be located to receive a sampled portion of the beam which passes through an aperture 236a of mirror 236.” (Bornhorst '921, col. 17, ln. 41-col. 18, ln. 2).
U.S. Pat. No. 6,211,627 to Callahan discloses: “A light/color meter provided with a data link link or interface to one can link to the corrector so that the beam can be automatically conformed to the specified values by appropriate adjustment of the scrolls, discs, and/or dowser”. (Callahan '627, col. 21, ln. 21-col. 21, ln. 25).
“The light/color meter and/or the ‘corrector’ can communicate via a hard-wired serial channel and/or a broadcast link. The measured values can be read at a location remote from the light meter(s), including at the fixture, and the user can actuate the scrolls, discs, or dowser from a variety of remote locations.” (Callahan '627, col. 21, lns. 25-31).
U.S. Pat. No. 7,014,336 to Ducharme discloses: “ . . . the calibration system includes a lighting fixture (2010) that is connected to a processor (2020) and which receives input from a light sensor or transducer (2034). The processor (2020) may be processor (316) or may be an additional or alternative processor. The sensor (2034) measures color characteristics, and optionally brightness, of the light output by the lighting fixture (2010) and/or the ambient light, and the processor (2020) varies the output of the lighting fixture (2010). Between these two devices modulating the brightness or color of the output and measuring the brightness and color of the output, the lighting fixture can be calibrated where the relative settings of the component illumination sources (or processor settings (2020)) are directly related to the output of the fixture (2010) (the light sensor (2034) settings). Since the sensor (2034) can detect the net spectrum produced by the lighting fixture, it can be used to provide a direct mapping by relating the output of the lighting fixture to the settings of the component LEDs.” (Ducharme '336, col. 15, ln. 46-col. 15, ln. 65).
U.S. Pat. No. 5,282,121 to Bornhorst shows the position of light sensitive electrical device 224 that may be positioned in the shadow of a gobo or other projected image. (Bornhorst, col., 17, lns. 50-55). Further a second color sensor or spectrum analyzer 280 may be located as to intercept light through an aperture 236a of mirror 236. (Bornhorst, '121, col. 17, ln. 63-col. 18, ln. 2)
It is known in the art that the light beams created by theatrical lights are seldom perfectly homogenous across the entire projected light. There can be differences in Correlated Color Temperature (CCT) by as much as two hundred and fifty degrees Kelvin from the center to the edge of the projected light beam. Unfortunately a sensor placed in the middle of beam is subject to only being able to measure a center sample of the light beam. The center of the light beam may have a visible significant color difference compared to the edge of the light beam. In this case any calibration or reference of the overall average color of the projected light of the theatre device would suffer the corresponding inaccuracies.
It is also know by the disclosure of U.S. Pat. No. 5,282,121 to Bornhorst the method of suspending a spectral sensor in the center of a theatrical light beam may cause the sensor to be positioned in a shadow or image. Finally a sensor positioned in the center of a light beam is subject to sensing only light from the center area of the light beam.